Al-Qaeda is training hundreds of British people fighting in Syria to become jihadists and urging them to carry out attacks when they return home, according to an interview with a defector published in Monday's Daily Telegraph.
The defector, known as Murad, from the hardline Islamic State of Iraq and al-Sham (ISIS) said other recruits from Europe and the US were also being trained to make car bombs before being sent home to form terror cells.
"They talked often about terrorist attacks," he said of his former ISIS instructors.
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"The foreigners were proud of 9/11 and the London bombings. The British, French and American mujahideen in the room started talking about places that they wanted to bomb or explode themselves in Europe and the United States.
"The American said he dreamed of blowing up the White House," he told the newspaper.
He called the teachings of ISIS, which grew out of Al-Qaeda's affiliate organisation in Iraq, "very hardline".
Britain's intelligence services estimate that around 500 British fighters are currently in Syria, and fear they will return radicalised.
Police on Friday charged two 21-year-old men from Birmingham, central England, with travelling to Syria to carry out acts of terrorism.